1H-Imidazol-3-ium-4-carboxyl­ate

In the title compound, C₄H₄N₂O₂, both imidazole N atoms are protonated and carboxyl­ate group is deprotonated, resulting in a zwitterion. The mol­ecule is essentially planar, with an r.m.s. deviation of 0.012 (1) Å. In the crystal, N—H...O hydrogen bonds and π–π stacking inter­actions [centroid–centroid distance = 3.674 (2) Å] between the imidazole rings link the mol­ecules into a three-dimensional supra­molecular network.